Microelectromechanical systems (MEMS) is a technology that can generally be described as miniaturized mechanical and electro-mechanical elements that are made using the techniques of microfabrication. The critical physical dimensions of MEMS devices can vary from well below one micrometer (micron) to several millimeters. Likewise, the types of MEMS devices can vary from relatively simple structures lacking any moving elements, to extremely complex electromechanical systems with multiple moving elements that are under the control of integrated microelectronics. Non-limiting examples of MEMS devices include sensors and optical devices, such as single-band or multi-band detector focal plane arrays (FPAs) or microbolometers. FPA devices may include single-band or multi-band integrated FPAs (e.g., single band visible FPA devices, or integrated dual-band FPA devices that are capable of detecting both near infrared (IR) spectrum radiation and visible spectrum radiation).
A microbolometer is an example of a MEMS device that can be used in an FPA. Microbolometers are devices that measure the power of incident electromagnetic radiation by heating material with a temperature-dependent electrical resistance. The resulting increase in temperature correlates to the energy of the absorbed radiation and is measured by a change of the electrical resistance of the bolometer thermistor material. The measurements may be made by any one of a number of temperature sensing techniques, including thermoelectric, pyroelectric, or resistive methods. The term “uncooled infrared bolometers” usually refers to resistive microbolometers where the temperature increase is measured by a change in resistance. These types of microbolometers may be used in commercial and military IR imaging applications.
Microbolometers are often fabricated using integrated circuit fabrication techniques. The basic construction includes a substrate that includes an FPA that comprises a plurality of detector elements that correspond to respective pixels. The substrate contains an integrated circuit which is electrically coupled to the detector elements, and is commonly known as a read out integrated circuit (ROIC). After fabrication, microbolometers are generally placed in vacuum packages to provide an isolated environment for the device. The vacuum package provides an optimal environment for the sensing device, since the presence of gas may impede performance. Alternatively, the bolometer may be packaged in a specific atmosphere comprising one or more gases.